1. Technical Field of the Invention
The present invention relates to novel water-in-oil emulsions, in particular to novel cosmetic compositions comprised thereof for the photoprotection of the skin and/or hair against the damaging effects of UV radiation, and which comprise the combination of two judiciously selected emulsifying agents.
2. Description of the Prior Art
It is known to this art that light radiation of wavelengths ranging from 280 nm to 400 nm promotes tanning of human skin and that radiation of wavelengths ranging from 280 nm to 320 nm, i.e., UV-B irradiation, causes erythemas and skin burns which can impair the development of a natural tan and/or bronzing. For these reasons and also for aesthetic reasons, continuous need exists for means for controlling such natural tanning/bronzing and, thus, for controlling the coloration of the skin. Hence, such UV-B radiation must be screened from the skin.
It is also known to this art that UV-A radiation, of wavelengths ranging from 320 nm to 400 nm, which causes the skin to tan, also adversely affects it, especially in the case of sensitive skin or skin which is continually exposed to solar radiation. In particular, UV-A radiation causes a loss of skin elasticity and the appearance of wrinkles, promoting premature skin aging. Such irradiation promotes the triggering of the erythemal reaction or accentuates this reaction in certain individuals and may even be the source of phototoxic or photoallergic reactions. Thus, for aesthetic and cosmetic reasons, such as preservation of the natural elasticity of the skin, for example, more and more subjects wish to control the effect of UV-A radiation on their skin. It is thus desirable to also screen out the UV-A radiation.
A wide variety of cosmetic and/or dermatological compositions for the photoprotection (UV-A and/or UV-B) of human skin are known to this art.
These photoprotective/sunscreen compositions are quite typically oil-in-water emulsions, namely, a cosmetically and/or dermatologically acceptable vehicle, diluent or carrier comprising a continuous aqueous dispersing phase and a discontinuous oily dispersed phase, due, in particular, to their pleasant feel (similar to water) and to their formulation as non-greasy milks or creams.
However, one of the disadvantages of oil-in-water emulsions is that they very easily lose their effectiveness with respect to UV protection as soon as they come into contact with water; this because the screening agents which they contain in their aqueous phase are removed by the water, during bathing in the sea or in swimming pools, for example, or, alternatively, under the shower or when playing water sports, and the overall photoprotective power of these compositions thus is greatly reduced.
Accordingly, in certain instances where a particularly high and lasting protection is desired, as for childrens' skin or for sensitive skin, it is preferable to employ water-in-oil compositions which exhibit good water persistence and which thus retain a very good photoprotective power even after bathing several times.
For such skin types, there is, in addition, a desire to minimize the risk of sensitization while avoiding, as far as possible, the presence within the formulations of active agents capable of causing skin reactions. Thus, need continues to exist for compositions which are simultaneously free of preservatives, while exhibiting an optimum stability which is maintained throughout the time of storage and ultimate use of the products.
Lastly, as these compositions are intended, in particular, to be topically applied onto the skin, they should also exhibit good cosmetic properties, namely, a good appearance, a good resistance to the immediate environment and, in the specific case of sunscreen compositions for children, nonadherence to sand, with which they are often in contact (beaches, play areas). These compositions should also spread easily and be pleasant in appearance.
Emulsions of water-in-oil type stabilized by silicone emulsifiers, such as dimethicone copolyols, which are well known for their good water-in-oil emulsifying properties, are known and are described, for example, in GB-2,242,358.